Choosing the right architectural style isn’t just a technical detail — it’s critical to the success of your API and every application that relies on it. The architecture determines how easily developers can understand and integrate your API, profoundly impacting their experience. It dictates how clients and servers communicate, directly affecting application efficiency, performance, and scalability. Plus, the style influences versioning, making it easier or harder for developers to manage changes.

To help you make this critical choice, we’ve highlighted four API architectural styles: REST, webhooks, gRPC, and HATEOAS. We chose these styles because each offers unique capabilities — efficient and cacheable data retrieval, asynchronous communication, multiple communication patterns, and dynamic discoverability, respectively. We’ll explain what each style is, why you would choose each one, and provide some real-world examples.

1. REST

Representational State Transfer (REST) APIs are resource-based, using HTTP methods such as GET, POST, DELETE, PUT, and PATCH. They typically return data in JSON format. Other format options include CSV, HTML, plain text, and XML.

When API designers discuss REST, they’re typically not referring to Roy Fielding’s complete definition of REST outlined in his dissertation published in 2000. According to Fielding, a proper REST API must adhere to the hypermedia as the engine of application state (HATEOAS) constraint. Many APIs today have elements of REST but don’t conform to HATEOAS.

Why Choose This Architectural Style?

According to Postman’s State of the API Report for 2025, REST continues to be the most popular API architectural style, with 93% of respondents choosing REST as the foundation for APIs that power web and mobile applications, third-party integrations, and general data retrieval.

Developers love the REST architectural style because it’s:

• Simple: Easy to use and understand (for humans and machines!)
• Stateless: All client-server interactions are independent tasks.
• Cacheable: Data can be cached to boost bandwidth and conserve server resources.
• Optimized for the internet: Enables the use of lightweight formats like JSON, which are easy for browsers and programs to parse.

REST is ideal for APIs that need to deliver standard web services and data or enable applications to perform tasks through CRUD operations. The ability to use easily parsable formats speeds up responses and improves application performance.

Examples of REST APIs in the Real World

Countless companies offer REST APIs. For example, Twilio’s APIs are organized around REST. Developers can use Twilio APIs to add various communication capabilities to their applications. Many of the APIs available through Microsoft Azure are REST, such as the Azure Storage REST API and the Azure Databricks REST API.

2. Webhooks

The webhook API architectural style involves delivering event-driven payloads via simple HTTP POST requests. Webhooks push data to applications or systems that then act on that data in real time.

Why Choose This Architectural Style?

Webhooks rank second (50%) on Postman’s list of commonly used API styles. Popular uses of webhook APIs include CI/CD pipelines, messaging apps, e-commerce platforms, and code collaboration platforms.
Developers often require webhook APIs for applications because they enable:

• Asynchronous communication: Applications receive information instantly when an event occurs. It doesn’t require constant polling to see if data is available.
• Automation: Systems can automatically send data and alerts based on specified triggers to external or internal applications.
• Enhanced user experiences: Users can receive automatic notifications and event-driven alerts. This allows them to stay updated on important events without having to regularly check for updates manually.

Developers use webhook APIs when they need an application to automatically send data based on a real-time event. For example, when an e-commerce website needs to send an order status update or a messaging app needs to alert the server that a user sent a message to a channel. Webhooks are ideal for building modern, reactive applications.

Examples of Webhook APIs in the Real World

Many companies rely on webhooks to power platforms and applications. GitHub provides webhooks so developers can create integrations that can take actions in response to events that occur on GitHub, such as new pull requests. Slack lets applications use incoming webhooks to send messages to channels on its platform.

3. gRPC

Initially developed by Google, gRPC is an open-source implementation of the Remote Procedure Call (RPC) API architectural style. It is currently maintained by the Cloud Native Computing Foundation (CNCF). gRPC uses the HTTP/2 protocol for transport, which enables bi-directional streaming.

Why Choose This Architectural Style?

gRPC is not as popular an architectural style as REST and webhooks, with only 14% of respondents to Postman’s survey saying they use it as the foundation for their APIs. However, developers often choose gRPC for their APIs because it is:

• Fast and efficient: gRPC serializes messages using Protobuf, which produces smaller message payloads that require less bandwidth.
• Flexible: It supports four communication patterns, which include unary, server streaming, client streaming, and bidirectional streaming.
• Secure: It has built-in auth mechanisms and pluggable auth, where you can plug in your own authentication systems.

gRPC is a great choice for developers building internal microservices-style architectures and connecting browser clients and mobile devices to backend services. It’s also ideal for applications that require high performance and low-latency APIs or involve streaming video or audio.

Examples of gRPC APIs in the Real World

As the creator of gRPC, Google offers many APIs with this architectural style. For example, the Google Cloud Pub/Sub API and Google Cloud Natural Language API surface gRPC interfaces. While Netflix doesn’t offer gRPC APIs to external developers, the company does rely heavily on them for backend-to-backend communication.

4. HATEOAS

HATEOAS is a well-established API design style and REST constraint. It allows developers to create self-descriptive APIs with embedded hypermedia links that clients can discover dynamically. Clients don’t have to know all the hardcoded API paths beforehand.

Why Choose This Architectural Style?

Few developers today opt for this architectural style when designing APIs. It didn’t even make it onto Postman’s 2025 State of the API report. So why would we highlight an API style that currently has little traction with API developers? Because hypermedia provides ways to address several AI agent problems. These problems involve tool calling, maintaining context, and managing runtime environments. Thanks to AI, HATEOAS could make a comeback.

There are plenty of reasons to design APIs with HATEOAS, such as:

• Flexibility: HATEOAS’ structure makes for highly flexible and backward-compatible APIs. It offers dynamic discoverability, which allows clients to adapt to API changes and new features without the need to modify code.
• Automation: It can enable automation of machine-to-machine communications, making it possible for a client to independently navigate paths from start to finish. GRAIL (Goal-Resolution through Affordance-Informed Logic) is an example of this automation.
• Workflow guidance: By providing links (affordances) that are dynamically generated based on the current state of a resource, hypermedia guides the client through complex business workflows (e.g., you can’t “ship” an order unless it’s been “paid”). These affordances ensure clients only attempt valid actions at any given time.

HATEOAS is a good choice for APIs that need to help consumers (humans or machines) discover available actions and related resources dynamically. And it is an excellent option if you want to ensure backward compatibility. Also, hypermedia is an effective way to accumulate the results of past choices by AI agents and constrain the potentially useful tools available for the next interaction.

As Darrell Miller, partner API architect at Microsoft, shares on LinkedIn, “AI agents don’t solve the hypermedia problem, but hypermedia does solve the AI agent problem of tool selection and efficiently maintaining context.”

Examples of HATEOAS APIs in the Real World

The most often cited real-world examples of HATEOAS are PayPal’s REST APIs. Some of these APIs return responses that include one or more contextual HATEOAS links. Clients can use these links to request more information related to a specific request and construct an API flow.

Choose an API Architectural Style Carefully

If you plan on designing an API, you need to carefully consider your choice of API architecture. That choice depends on the services and capabilities your API will expose. It also depends on the types of applications you expect to consume the API. The RESTful style remains the most used architecture in API design. However, requirements for real-time events, low latency, or discoverability may mean webhooks, gRPC, or HATEOAS are best suited for the job.

We didn’t include GraphQL in the list because it’s not an API architecture but instead a query language and runtime for APIs. However, you should consider GraphQL when designing your APIs, as it can improve data retrieval efficiency.

We also didn’t include websockets, server-sent events (SSE), MQTT, or AMQP, as they are not API architectural styles but communication and messaging protocols. That said, consider one of these protocols if you need your API to facilitate real-time or asynchronous data exchange.

Now that you know what to look for in an architectural style, you’re ready to approach your next API design project!